The present invention relates in general to dynamoelectric machines and, more particularly, to a stacked generator stator frame assembly adapted to reduce production cycle time, eliminate stacking rework and simplify the core construction. Thus, the present invention discloses an apparatus and method for mechanically coupling stator core lamination sectors to a stator frame.
To better understand the unique and advantageous features of the invention, it is helpful to have an understanding of conventional structures that provide this function. Exemplary such conventional apparatus are disclosed for example in U.S. Pat. Nos. 4,564,779 and 4,837,471, the entire disclosures of each of which are incorporated herein by this reference.
Referring to FIG. 1, a portion of a conventional stator 10 is shown and includes a generally annular stator frame formed by an outer wrapper plate 12 and a plurality of annular web plates 14, only one of which is shown in FIG. 1 for clarity. Holes 16 are bored in the annular web plate 14 sufficiently close to the radially inner edge 18 so that part circular holes result. A plurality of keybars 20 are disposed in respective holes 16. The keybars are used to attach the lamination sectors 22 to the web plates 14. More specifically, the keybars 20 each have a cylindrical portion 24 which is disposed within the holes 16 of the annual web plates 14 and a dovetail portion 26 which extends radially inwardly from the cylindrical portion 24. The dovetail portions 26 of the keybars mate with respective dovetail slots 28 in the radially outer curved edge 30 of stator core lamination sectors 22. The portion of stator 10 shown in FIG. 1 includes several of the plurality of stator slots 32 which contain conventional current carrying conductors 34 (only one occupied slot being shown in FIG. 1 for ease of illustration). The conductors are held in the respective slot by a conventional dovetail retaining wedge (not shown). The stator core is actually built up by stacking large numbers of stator core lamination sectors 22 side by side in sandwiched-like relationship along the dovetails of the keybars. Generally, the sectors are segmental insulated laminations of silicon steel, each typically on the order of 0.3 to 0.5 mm thick. In the illustrated construction of stator 10, the annular web plates 14 are rigidly fixed to outer wrapper plate 12 using weld beads 36.
The above described generator stator frame design requires the frame application and machining be completed prior to cleaning and stacking. Keybars, either welded or bolted in the frame have dovetail locations which require very tight position tolerances to ensure stackablity. The frames are stacked by hand by rocking each core punching/lamination onto the keybar dovetail at axial slot positions located every 14 inches along the axial length of the keybar. The current method of producing stacked stator frames has little margin for fabrication/machining error and often results in rework and extended stacking cycle time.
The invention is embodied in a stator cage design that allows parallel manufacturing of the stator frame and core, thereby reducing cycle time. The core is formed by stacking a plurality of laminations, each defined by a plurality of lamination sectors that each have one or more grooves or cutouts defined at spaced locations about the outer periphery thereof. The grooves or cutouts of axially adjacent laminations are aligned to define longitudinal grooves for receiving keybars, each of which preferably has a generally circular cross section. Core flanges are disposed at least at each longitudinal end of the stacked laminations and include a plurality of apertures therethrough for receiving the respective keybars. Compression bands are circumferentially disposed about the stacked lamination and keybar assembly to hold the keybars in the circumferential groves of the laminations thereby arch-binding the core, radially locking the stacked laminations. The core is then concentrically assembled into a stator frame. The stator frame includes frame support plates for being bolted to the flanges of the stator core and radially extending frame section plates disposed at spaced locations along the length thereof between the frame support plates. The radially compressed core assures that the core punchings/lamination sectors remain in position with no binding agent required. Since there is no gap between the adjacent lamination sectors, they are self locking under radial compression. Moreover, by providing round keybars with no dovetails, in accordance with a preferred embodiment, and pressing them against complimentarily circular depressions on the core outer surface, the keybars are self located. The radial fit between the keybar and core depression assures no back of core chatter which can occur with traditional keybar dovetails creating noise and excessive core to keybar dovetail clearances.